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Biomedical subjects

S P Levine

Publications and source records attributed to S P Levine.

At least 19 recordsLinked to original sources
PubMed2003

Spatiotemporal patterns of beta desynchronization and gamma synchronization in corticographic data during self-paced movement.

OBJECTIVE: To study the spatiotemporal pattern of event-related desynchronization (ERD) and event-related synchronization (ERS) in electrocorticographic (ECoG) data with closely spaced electrodes. METHODS: Four patients with epilepsy performed self-paced hand movements. The ERD/ERS was quantified and displayed in the form of time-frequency maps. RESULTS: In all subjects, a significant beta ERD with embedded gamma ERS was found. CONCLUSIONS: Self-paced movement is accompanied not only by a relatively widespread mu and beta ERD, but also by a more focused gamma ERS in the 60-90 Hz frequency band.

Adult↗
PubMed2002

Visualization of significant ERD/ERS patterns in multichannel EEG and ECoG data.

OBJECTIVES: Analysis of event-related desynchronization (ERD) and event-related synchronization (ERS) often requires the investigation of diverse frequency bands. Such analysis can be difficult, especially when using multichannel data. Therefore, an effective method for the visualization of event-related changes in oscillatory brain activity is required. METHODS: A bootstrap-based method is presented which gives time-frequency maps showing only significant changes of ERD or ERS in predetermined frequency bands. RESULTS: Examples from an electroencephalographic study and an electrocorticographic study are shown. The results demonstrate how easily reactive channels and their spatio-temporal and frequency-specific characteristics can be identified by means of this method. CONCLUSIONS: The proposed method is a simple but effective way to visualize significant ERD/ERS patterns.

Algorithms↗
PubMed2000

Electrical stimulation for pressure sore prevention and wound healing.

This paper reviews applications of therapeutic electrical stimulation (ES) specific to wound healing and pressure sore prevention. The application of ES for wound healing has been found to increase the rate of healing by more than 50%. Furthermore, the total number of wounds healed is also increased. However, optimal delivery techniques for ES therapy have not been established to date. A study of stimulation current effects on wound healing in a pig model has shown that direct current (DC) stimulation is most effective in wound area reduction and alternating current (AC) stimulation for wound volume reduction at current densities of 127 microA/cm2 and 1,125 microA/cm2, respectively. Preliminary studies have been carried out at two research centers to assess the role of ES in pressure sore prevention. Surface stimulation studies have shown that ES can produce positive short-term changes in tissue health variables such as regional blood flow and pressure distribution. The use of an implanted stimulation system consisting of intramuscular electrodes with percutaneous leads has been found to produce additional long-term changes. Specifically, gluteal muscle thickness increased by 50% with regular long-term ES application concurrent with a 20% decrease in regional interface pressures and increased tissue oxygen levels. These findings indicate that an implantable ES system may have great potential for pressure sore prevention, particularly for individuals who lack sensation or who are physically unable to perform regular independent pressure relief.

Aged↗
PubMed2000

Tomographic reconstruction of tracer gas concentration profiles in a room with the use of a single OP-FTIR and two iterative algorithms: ART and PWLS.

Computed tomographic (CT) reconstructions of air contaminant concentration fields were conducted in a room-sized chamber employing a single open-path Fourier transform infrared (OP-FTIR) instrument and a combination of 52 flat mirrors and 4 retroreflectors. A total of 56 beam path data were repeatedly collected for around 1 hr while maintaining a stable concentration gradient. The plane of the room was divided into 195 pixels (13 x 15) for reconstruction. The algebraic reconstruction technique (ART) failed to reconstruct the original concentration gradient patterns for most cases. These poor results were caused by the "highly underdetermined condition" in which the number of unknown values (156 pixels) exceeds that of known data (56 path integral concentrations) in the experimental setting. A new CT algorithm, called the penalized weighted least-squares (PWLS), was applied to remedy this condition. The peak locations were correctly positioned in the PWLS-CT reconstructions. A notable feature of the PWLS-CT reconstructions was a significant reduction of highly irregular noise peaks found in the ART-CT reconstructions. However, the peak heights were slightly reduced in the PWLS-CT reconstructions due to the nature of the PWLS algorithm. PWLS could converge on the original concentration gradient even when a fairly high error was embedded into some experimentally measured path integral concentrations. It was also found in the simulation tests that the PWLS algorithm was very robust with respect to random errors in the path integral concentrations. This beam geometry and the use of a single OP-FTIR scanning system, in combination with the PWLS algorithm, is a system applicable to both environmental and industrial settings.

Air Pollution, Indoor↗
PubMed2000

A direct brain interface based on event-related potentials.

Cross-correlation between a trigger-averaged event-related potential (ERP) template and continuous electrocorticogram was used to detect movement-related ERP's. The accuracy of ERP detection for the five best subjects (of 17 studied), had hit percentages >90% and false positive percentages <10%. These cases were considered appropriate for operation of a direct brain interface.

Adult↗
PubMed1999

Identification of electrocorticogram patterns as the basis for a direct brain interface.

This study reports on the first step in the development of a direct brain interface based on the identification of event-related potentials (ERPs) from an electrocorticogram obtained from the surface of the cortex. Ten epilepsy surgery patients, undergoing monitoring with subdural electrode strips and grid arrays, participated in this study. Electrocorticograms were continuously recorded while subjects performed multiple repetitions for each of several motor actions. ERP templates were identified from action-triggered electrocorticogram averages using an amplitude criterion. At least one ERP template was identified for all 10 subjects and in 56% of all electrode-recording sets resulting from a subject performing an action. These results were obtained with electrodes placed solely for clinical purposes and not for research needs. Eighty-two percent of the identified ERPs began before the trigger, indicating the presence of premovement ERP components. The regions yielding the highest probability of valid ERP identification were the sensorimotor cortex (precentral and postcentral gyri) and anterior frontal lobe, although a number were recorded from other areas as well. The recording locations for multiple ERPs arising from the performance of a specific action were usually found on close-by electrodes. ERPs associated with different actions were occasionally identified from the same recording site but often had noticeably different characteristics. The results of this study support the use of ERPs recorded from the cortical surface as a basis for a direct brain interface.

Cerebral Cortex↗
PubMed1999

Detection of event-related potentials for development of a direct brain interface.

The study presented here is part of an ongoing effort to develop a direct brain interface based on detection of event-related potentials (ERPs). In a study presented in a companion article, averaged ERP templates were identified from electrocorticograms recorded during repetition of voluntary motor actions. Here the authors report on the detection of individual motor ERPs within the electrocorticogram using cross-correlation. An averaged ERP template was created from the first half of each electrocorticogram and then cross-correlated with the continuous electrocorticogram from the second half. Points where the cross-correlation value exceeded an experimentally determined detection threshold were considered to be detection points. A detection point was considered to be a valid "hit" if it occurred between 1 second before and 0.25 second after the recorded time of a voluntary action. The difference between the hit and false-positive percentages (HF-difference) was used as a metric of detection accuracy. HF-differences greater than 90 were found for 5 of 15 subjects, HF-differences greater than 75 were found for 8 of 15 subjects, and HF-differences greater than 50 were found for 12 of 15 subjects. The three other subjects with HF-differences less than 50 had electrode locations not well suited for recording movement-related ERPs. Recordings from sensorimotor and supplementary motor areas produced the highest yield of channels with HF-difference greater than 50; however, a number of channels with good performance were found in other areas as well. The results demonstrate the likely prospect of using ERP detection as the basis of a single-switch direct brain interface and that furthermore, there is a good possibility of obtaining multiple control channels using this approach.

Analysis of Variance↗
PubMed1999

The NavChair Assistive Wheelchair Navigation System.

The NavChair Assistive Wheelchair Navigation System [19] is being developed to reduce the cognitive and physical requirements of operating a power wheelchair for people with wide ranging impairments that limit their access to powered mobility. The NavChair is based on a commercial wheelchair system with the addition of a DOS-based computer system, ultrasonic sensors, and an interface module interposed between the joystick and power module of the wheelchair. The obstacle avoidance routines used by the NavChair in conjunction with the ultrasonic sensors are modifications of methods originally used in mobile robotics research. The NavChair currently employs three operating modes: general obstacle avoidance, door passage, and automatic wall following. Results from performance testing of these three operating modes demonstrate their functionality. In additional to advancing the technology of smart wheelchairs, the NavChair has application to the development and testing of "shared control" systems where a human and machine share control of a system and the machine can automatically adapt to human behaviors.

Algorithms↗
PubMed1999

Automatic adaptation in the NavChair Assistive Wheelchair Navigation System.

The NavChair Assistive Wheelchair Navigation System [7] is an adaptive shared control system being developed to provide mobility to those individuals who would otherwise find it difficult or impossible to use a power wheelchair due to cognitive, perceptual, or motor impairments. The NavChair provides task-specific navigation assistance to the wheelchair operator in the form of several distinct operating modes, each of which distributes control differently between the wheelchair and the operator. This paper describes the NavChair's mechanism for automatically selecting the most appropriate operating mode based on a combination of the wheelchair's immediate situation and its global location. Results from two experimental evaluations of the adaptation method are presented.

Adult↗
PubMed1999

Progress in characterization of pre-implantation factor in embryo cultures and in vivo.

PROBLEM: Pre-implantation factor (PIF), a small, embryo-derived peptide is detected in the maternal serum prior to implantation and is associated with successful pregnancy outcome. However, its identity is not known. METHOD OF STUDY: PIF was isolated from mouse embryo conditioned media and from pregnant porcine sera, using high-performance liquid chromatography (HPLC) followed by mass spectrometry. RESULTS: Conditioned culture media was separated by gel filtration chromatography followed by reversed phase chromatography. At each step, PIF activity was determined by the lymphocyte/platelet binding autorosette assay (LPBA). Mass spectrometry yielded a single peak with a mass of 1300 Da. The peptide is, however, present in very low concentrations (fM), which has so far precluded complete identification. Pregnant porcine sera that exhibit potent PIF activity were deproteinated by acetone and further fractionated by reversed phase HPLC. Active fractions contain peptides of molecular masses 523 and 551 Da. CONCLUSION: PIF, likely to be peptides, represents a novel substance related to pregnancy initiation and maintenance.

Animals↗
PubMed1998

Activity-based cost management. Part II: Applied to a respiratory protection program.

To demonstrate the relevance of activity-based cost management (ABCM) for the occupational and environmental health community, the investigators used data generated by an ABCM model of a respiratory protection program (RPP) to develop options for solving a business problem. The RPP manager in this hypothetical but realistic business scenario is faced with a 25% budget cut and a 10% increase in demand for RPP services. The manager's dilemma is to maintain the integrity of the RPP while absorbing a significant budget cut. Various cost savings options are developed, and the assumptions under which these options operate are presented. It is emphasized that the RPP manager's primary responsibility is to assure worker health and safety by first understanding the technical issues, merits, and implications of any cost-cutting option that may be considered. It is argued that only then should the manager consider the financial merits of the possible solutions to this business problem. In this way worker health and safety, and environmental protection goals, can continue to be achieved in an economic climate of cost cutting and downsizing.

Accounting↗
PubMed1998

Field validation of passive monitors for the determination of employee exposures to methylene chloride in pharmaceutical production facilities.

A series of field evaluations was performed to estimate the overall uncertainty of three manufacturers' passive monitors (Assay Technology Model 541 and 546, 3M Model 3520, and SKC Model 575-001) to determine methylene chloride (MeCl2) concentrations. Area samples were exposed in a pharmaceutical production facility at five MeCl2 air concentrations for both permissible exposure limit (PEL) and short-term exposure limit (STEL) periods. A specially designed evaluation chamber was used to concurrently expose six of each type of passive monitor while concurrently collecting six active samples from locations surrounding the dosimeter array. The active samples were used to estimate the actual concentration during the evaluation period. The precision, bias, and overall uncertainty were estimated for each monitor type at concentrations bracketing the Occupational Safety and Health Administration proposed exposure limits. The actual MeCl2 concentrations for the PEL sampling periods ranged from 0.9 to 63 ppm. The pooled overall uncertainty results for all the passive monitors evaluated under PEL sampling conditions met the NIOSH accuracy recommendations. Pooled overall uncertainty for PEL evaluations for the monitors were: Assay Technology Model 546 +/- 17%; 3M +/- 13%; and SKC +/- 17%. Actual MeCl2 concentrations for the STEL sampling periods ranged from 14 to 357 ppm. Pooled overall uncertainty results for Assay Technology and 3M monitors evaluated under STEL sampling conditions met the NIOSH accuracy recommendations; however, the SKC passive monitor was slightly greater than the NIOSH recommendation. Pooled overall uncertainty for STEL evaluations for the monitors were: Assay Technology Model 541 +/- 18%; 3M +/- 16%; and SKC +/- 27%.

Air Pollutants, Occupational↗
PubMed1998

Comparison of AIHA ISO 9001-based occupational health and safety management system guidance document with a manufacturer's occupational health and safety assessment instrument.

Numerous manufacturing and service organizations have integrated or are considering integration of their respective occupational health and safety management and audit systems into the International Organization for Standardization-based (ISO) audit-driven Quality Management Systems (ISO 9000) or Environmental Management Systems (ISO 14000) models. Companies considering one of these options will likely need to identify and evaluate several key factors before embarking on such efforts. The purpose of this article is to identify and address the key factors through a case study approach. Qualitative and quantitative comparisons of the key features of the American Industrial Hygiene Association ISO-9001 harmonized Occupational Health and Safety Management System with The Goodyear Tire & Rubber Co. management and audit system were conducted. The comparisons showed that the two management systems and their respective audit protocols, although structured differently, were not substantially statistically dissimilar in content. The authors recommend that future studies continue to evaluate the advantages and disadvantages of various audit protocols. Ideally, these studies would identify those audit outcome measures that can be reliably correlated with health and safety performance.

Environmental Monitoring↗
PubMed1998

Analysis of third-party certification approaches using an occupational health and safety conformity-assessment model.

The occupational health and safety conformity-assessment model presented in this article was developed (1) to analyze 22 public and private programs to determine the extent to which these programs use third parties in conformity-assessment determinations, and (2) to establish a framework to guide future policy developments related to the use of third parties in occupational health and safety conformity-assessment activities. The units of analysis for this study included select Occupational Safety and Health Administration programs and standards, International Organization for Standardization-based standards and guidelines, and standards and guidelines developed by nongovernmental bodies. The model is based on a 15-cell matrix that categorizes first-, second-, and third-party activities in terms of assessment, accreditation, and accreditation-recognition activities. The third-party component of the model has three categories: industrial hygiene/safety testing and sampling; product, equipment, and laboratory certification; and, occupational health and safety management system registration/certification. Using the model, 16 of the 22 programs were found to have a third-party component in their conformity-assessment structure. The analysis revealed that (1) the model provides a useful means to describe and analyze various third-party approaches, (2) the model needs modification to capture aspects of traditional governmental conformity-assessment/enforcement activities, and (3) several existing third-party conformity-assessment systems offer robust models that can guide future third-party policy formulation and implementation activities.

Accreditation↗
PubMed1997

Platelet alpha granule deficiency associated with decreased P-selectin and selective impairment of thrombin-induced activation in a new patient with gray platelet syndrome (alpha-storage pool deficiency).

We report studies on a new patient with gray platelet syndrome (GPS, alpha-storage pool deficiency). Her lifelong bleeding history is associated with platelet abnormalities characteristic of GPS including mild to moderate thrombocytopenia, a population of abnormally large platelets, and specific deficiencies of alpha-granule constituents and morphologically typical alpha-granules. Platelet function studies showed normal aggregation responses to adenosine diphosphate, epinephrine, collagen, arachidonate, and ristocetin but impaired activation responses to thrombin and a thrombin receptor-activating peptide (T1 peptide). These impaired responses included T1 peptide-induced aggregation, thrombin-induced adenine nucleotide secretion, and thrombin-induced (Ca2+)i increases. The impairment of the thrombin-induced (Ca2+)i increase was observed as a substantially slower initial rise in (Ca2+)i levels and a smaller maximum (Ca2+)i increase compared with the responses obtained in normal platelets and are thus similar to those reported previously in another patients with GPS. Flow cytometric measurements of the binding of two distinct monoclonal antibodies against the functional thrombin receptor indicated the presence of a normal number of receptors and normal receptor cleavage by thrombin in the GPS platelets, providing additional support for the hypothesis presented in previous studies that the thrombin activation defect in GPS platelets occurs subsequent to the interaction of thrombin with its receptor. The alpha-granule deficiency in this patient was associated with an approximately 50% decrease in the content and surface expression of the alpha-granule membrane-specific protein P-selectin in contrast to a previous report of normal amounts of P-selectin in the platelets of two related patients with GPS. This finding raises the possibility that the alpha-granule deficiency in GPS may be expressed in different phenotypes characterized by differences in the amount or constitution of residual alpha-granule membranes present in GPS platelets.

Adenosine↗
PubMed1997

Evaluation of virtual source beam configurations for rapid tomographic reconstruction of gas and vapor concentrations in workplaces.

Beam path average data from an Open Path Fourier Transform Infrared (OP-FTIR) spectrometer can be used to reconstruct two-dimensional concentration maps of the gas and vapor contaminants in workplaces and the environment using computed tomographic (CT) techniques. However, a practical limitation arises because in the past, multiple-source and detector units were required to produce a sufficient number of intersecting beam paths in order to reconstruct concentration maps. Such a system can be applied to actual field monitoring situations only with great expense and difficulty. A single monostatic OP-FTIR system capable of rapid beam movement can eliminate this deficiency. Instead of many source and detector units, a virtual source arrangement has been proposed using a number of flat mirrors and retroreflectors to obtain intersecting folded beam paths. Three virtual source beam configurations generated for a single-beam steerable FTIR system were tested using 54 flat mirrors and four retroreflectors or 54 flat mirrors and 56 retroreflectors mounted along the perimeter walls of a typical 24- x 21-ft test room. The virtual source CT configurations were numerically evaluated using concentration maps created from tracer gas concentration distributions measured experimentally in a test chamber. Synthetic beam path integral data were calculated from the test maps and beam configurations. Computer simulations of different beam configurations were used to determine the effects of beam geometry. The effects of noise and peak reducing artifacts were evaluated. The performance of the tomographic reconstruction strategy was tested as a function of concentration and concentration gradients.

Air Pollution, Indoor↗
PubMed1997

Quality control for industrial hygiene laboratories.

In the Republic of Korea a quality control programme has been introduced for industrial hygiene laboratories responsible for monitoring chemicals in working environments. Its development is outlined below.

Asbestos↗